1. Field of the Invention
The present invention relates to a system for metering flow velocity. More particularly, the present invention relates to a system that measures acoustic pulses in a flowing fluid. In particular, the present invention relates to a velocimeter and a method of comparing acoustic transmission delays between at least two velicometers.
2. Relevant Technology
Many fluid flow applications require real-time evaluation for various reasons such as fluid quality evaluation and process control. Such real-time evaluation allows for dynamic control and monitoring of the fluid flow application. The evaluation of fluid flow in a conduit may be due to the need to control, monitor, or adjust the dynamic volume of fluid being delivered through the conduit. Measuring the flow in a conduit is useful in a number of applications.
One such application is measuring the flow of water through an irrigation pipe, particularly in commercial irrigation applications. Flow measurement is useful for several reasons, including the ability to track the amount of water delivered to a portion of land in order to provide adequate irrigation. Additionally, where irrigation is used, water needs to be employed efficiently. For such reasons, irrigation systems require the ability to monitor the volumetric delivery of water and to measure flow rate.
Another application is measuring the flow of natural gas through a pipe, particularly as it is delivered from the gas fields to metropolitan areas. Measuring both the flow and the concentration of gas is useful for several reasons including the ability to track the total amount of gas being delivered from the gas fields as a response to consumer demand.
Closer to the end use, the monitoring of natural gas as it is mixed with ambient air and charged to a combustion device, may be critical for proper operation of the device. As gas flow meters typically measure a pressure drop such as by using the Venturi principle, the pressure drop may adversely affect the combustion device.
A number of devices for measuring flow rate exist for various applications. The size of the conduit being used, accuracy, cost, and other factors may play a role in determining what type of measuring device will be used for a specific application. One flow metering system uses differential pressures that are detectable with pressure transducers. Measuring flow in this manner requires the conduit to contract. Typical systems for contracting the flow profile include installing a section of pipe which tapers to a significantly smaller diameter.
The contraction of the flow of water through an irrigation pipe is undesirable for a number of reasons. For example, irrigation water often contains debris which can cause an obstruction in a small diameter pipe or which can become caught against a restriction. An obstruction will result in plugging of the pipe, requiring time, energy, and expense to unplug or otherwise repair it. In addition, time required to reverse plugging may jeopardize crops which go unwatered during unscheduled down time.
Another problem with differential pressure producing devices is that there is often significant retrofitting required to incorporate them into the system where flow is being measured. For example, in the case of devices which use a gradual reduction in the diameter of the conduit, a relatively long section of conduit must be removed and replaced with a tapering conduit section.
Another problem with measuring flow in a conduit is that variations in temperature and humidity can adversely affect detection conditions. These are often the types of conditions of commercial irrigation applications. More pronounced is the effect of temperature and humidity variations upon gaseous flow due to the tendency of the gas to expand or contract, and to change in quality where humidity is different between the gas source and the delivery point.
Another approach to measuring flow rate is the so-called elbow flow meter in which a curved section of pipe in the fluid delivery system is fitted with pressure sensors to measure pressure differential in the elbow. In order to measure the flow accurately, the sensors must be precisely placed in both the outer and inner circumferential walls of the elbow, in the same radial plane, and then must be calibrated.
The elbow flow meter itself, however, presents problems of its own. Initially, the mere fact that an elbow must be put into a pipe requires designing the pipe with a bend therein, or removing a section of the pipe to put a first elbow that diverts the flow direction, and a second elbow that restores the flow direction. The elbow flow meter may be configured with pressure transducers that measure the pressure of the fluid both before and after the elbow.
One problem occurs where transducers are located at different elevational levels, particularly for liquids, such that a slight pressure measurement bias is introduced due to the elevation difference. An elevation difference therefore requires calibration of the pressure transducers. Two or more transducers may be placed at each location both above and below the elbow but this requires averaging of the pressure measurements and a single malfunctioning pressure transducer will give a spurious average.
Another problem with elbow flow meters is the disturbance caused by the elbow bend itself that creates eddies, and other turbulence that may cause a spurious pressure reading downstream from the bend. As such, under certain flow regimes such as the laminar flow- to the laminar-to-turbulent-transition region, the disturbance at the bend may require the downstream transducer to be placed at a significant distance, thus complicating configuration of the flow meter. Additionally, where flow velocity variations may vary significantly between laminar and fully turbulent flow, the placement of a downstream transducer at a single location will be inadequate to monitor pressure drop for all flow regimes.
What is needed in the art is a fluid flow meter that avoids the problems of the prior art. Additionally, what is needed in the art is a fluid flow meter that does not require the obstruction or constriction of the flow in the conduit. What is also needed in the art is a fluid flow meter that does not require redirecting the flow of the fluids such as with an elbow and the like.
Such systems, methods, and apparatuses are disclosed and claimed herein.
The present invention relates to a system for measuring fluid flow that avoids the problems of the prior art. The inventive system uses a plurality of xe2x80x9csing-aroundxe2x80x9d circuits that may filter out capacitive couplings for gaseous systems and that filter out electronic noise for fluid systems in general.
The inventive system uses at least two non-intrusive sing-around circuits that send an audio signal through the flowing fluid within a conduit. A first sing-around circuit sends an audio signal in a direction perpendicular to the flow of the fluid. A second sing-around circuit sends an audio signal in a direction that is oblique to the direction of flow of the fluid in the conduit. Although such variables as fluid density, fluid temperature, fluid pressure, and fluid velocity must be monitored during ordinary metering of fluid flow, the inventive combination of the two sing-around circuits eliminates the need to monitor fluid density, fluid temperature, and fluid pressure.
Transit time for a signal to move a known distance between a transmitter and a receiver is determined for two separate sing-around circuits. Thereby, the transit-time shift velocity or sound velocity difference is determinable due to the fluid flow velocity. From the transit-time shift velocity, the flow velocity can be determined by understanding the trigonometric relationship between directional placement of each transmitter and receiver.
In the inventive circuit, an audio signal is generated from a transmitter and detected by a receiver. A portion of the audio signal reaches the receiver. The audio signal is converted into an electronic signal that is sent to a triggering system. The electronic signal may be boosted by an amplification circuit sufficient to create a triggering signal.
In the triggering system, the electronic signal may be amplified to assist in overcoming attenuation of the audio signal. Following optional amplification, the signal is rectified and gathered into a substantially half wave form. Spurious signals that are generated are filtered out by a gate or digital filter. The digital filter is tuned to anticipate approximately the time period when actual signals should pass therethrough and the digital filter simply eliminates any other signals that come outside the anticipated signal time window. Following digital filtration, the wave form is converted into a square wave and optionally changed in pulse width to optimize it as a triggering signal. The triggering signal is then ultimately sent to a pulser that instructs the transmitter to generate another audio signal.
A xe2x80x9ckeep-alivexe2x80x9d circuit is also provided in the sing-around loop for the occasion where no signal is detected to be cycling within the loop. The keep-alive circuit is configured to look for a pulse coming from upstream in the circuit loop. It looks for a pulse of a particular waveform, namely the square wave, and of a particular pulse width that is characteristic of that which was made of the circuit following digital filtration and conversion into a square wave. Where the anticipated signal is not received within a particular time window, the xe2x80x9ckeep-alivexe2x80x9d circuit generates its own signal, directed to the pulser, that instructs the transmitter to generate another audio signal in the direction of the receiver.
In any event, a pulse signal is generated and directed to the transmitter. At this point, a new audio signal is generated from the transmitter and detected by the receiver. After a number of cycles, the xe2x80x9csing-aroundxe2x80x9d circuit settles down to its designed cycling time. The amount of time required to relay the signal from the receiver around to the transmitter is known. The largest time lapse in the circuit is the time required for the audio signal to bridge the distance between the transmitter and the receiver. As such, the speed of sound in the known multiple-component fluid can be extracted from the total cycling time of the circuit.
It is therefore an object of an embodiment of the present invention to provide a system that overcomes the problems of the prior art. It is also an object of an embodiment of the present invention to provide a system for the measurement of fluid flow in a conduit without constricting or redirecting the flow of the fluid.
It is also an object of an embodiment of the present invention to provide a sing-around circuit to measure flow of a fluid that filters all spurious signals.
It is also an object of an embodiment of the present invention to provide a system for measurement of flow of a fluid that is being used in a dynamic system. It is also an object of an embodiment of the present invention to provide a system for the measurement and control of fluid flow that is being conveyed in a conduit.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.